In a system, such as a so-called electronic commerce or the like, that presents a product to a user via a network or the like, products for sales are classified into categories and registered in a database. As a use of categories, as shown in the basic classification table in Patent Literature 1, categories for classified products are strictly defined in advance so that products are automatically classified into categories. However, in actuality, it is generally arranged such that categories can be registered with flexibility, depending on a situation of sales of products, so that products can be classified into categories at shop's discretion. In a system that provides information, such as cooking information, accommodation facility information, or the like, as well, it is generally a case that objects of information to be provided are classified into categories by an information provider.